Telomeres are the nucleoprotein complexes that make up the ends of chromosomes in eukaryotes. We have solved the crystal structure, at modest resolution, for three different complexes formed by the 0. nova telomere end binding protein and single stand DNA. One of these complexes, formed as a ternary complex of the alpha subunit, the beta subunit, and a 12-ntd ssDNA, represents the authentic 3' terminus of the telomere (2.8 A, Horvath et al., 1998). A second complex is formed by the alpha subunit alone and ssDNA (2.8 A, Peersen unpublished) and a third is assembled as the alpha subunit N terminal, DNA-binding domain and ssDNA (3.2 A, Classen, unpublished). Together, these complexes highlight the varied interactions that may form during assembly of the natural telomere complex. Additionally, nucleotide substitution variants of the alpha:beta:ssDNA complex have been crystallized providing an opportunity to test the role that certain interactions play in sequence specific recognition of ssDNA within the telomere complex. Our aim is to collect higher resolution data for these telomere complexes. Poliovirus RNA dependent RNA polymerase: Small positive strand RNA viruses such as rhinovirus, hepatitis A, and polio are important pathogens. At the center of the life cycle for these viruses is an RNA-dependent RNA polymerase. We have solved the structure of the poliovirus RNA polymerase to 2.6 A resolution (Hansen, 1997), the first and only structure in this class of RNA-to-RNA polymerases which comprises over 4, 100 known or putative members. Crystals were originally prepared under high salt conditions (2M CaCl). More recently an alternate crystal form has been prepared by transferring these high-salt crystals into low salt. The alternate form exhibits a doubling of the unit cell c axis and a switch in the handedness of the 3 fold screw axis. Additionally, a conformational switch is observed in one region of the polymerase which likely relates to the function of this enzyme. Both crystal forms reveal extensive polymerase-polymerase interactions which we believe are important for RN A binding and replication activity. Our aim is to collect higher resolution data for both the high and low salt forms of the poliovirus polymerase. Data was collected on BioCARS Station 14 BM-C.